The present invention relates to a hydraulic suspension system for a vehicle. The present invention also relates to a vehicle being provided with a hydraulic suspension system and a method for damping an anti-roll function of a hydraulic suspension system for a vehicle.
The invention is applicable on working machines within the fields of industrial construction machines or construction equipment; in particular articulated haulers. Although the invention will be described with respect to an articulated hauler, the invention is not restricted to this particular vehicle, but may also be used in working machines, such as wheel loaders and backhoe loaders. It may also be used in e.g. trucks, buses or cars.
Vehicles, for example articulated haulers, today are most often provided with suspension systems in order to e.g. provide for a better travel comfort by absorbing e.g. road irregularities, bumps and ledges. An articulated hauler is provided with a dump body or container for carrying and transporting a load. An articulated hauler may be operated with large and heavy loads, for example for transports in connection with road or tunnel buildings, sand pits, mines and similar environments.
In some vehicles, the suspension systems are of hydraulic type. In such systems, a hydraulic suspension cylinder may be provided to each wheel of the vehicle. In order to reduce the body roll of the vehicle during fast cornering or when travelling over road irregularities, anti-roll systems may be provided in relation to the suspension system. For hydraulic suspension systems, the anti-roll systems may be provided by cross-coupling two hydraulic suspension cylinders. Hence, a first chamber of a first hydraulic cylinder may be in fluid communication with a second chamber of a second hydraulic cylinder and a second chamber of the first hydraulic cylinder may then be in fluid communication with a first chamber of the second hydraulic cylinder. The cross-connection then works as a hydraulic anti-roll bar. Such a hydraulic anti-roll bar functions works well for some driving conditions, while it has a tendency to increase the sideways rolling, or lateral vibrations, of the vehicle in other driving conditions, such as when driving over an obstacle with one or more of the wheels of one side of the vehicle.
It is desirable to provide a hydraulic suspension system having both satisfactory anti-roll functionality and satisfactory prevention of lateral vibrations.
The hydraulic suspension system for a vehicle according to an aspect of the invention comprises at least a first hydraulic cylinder and a second hydraulic cylinder, each of said hydraulic cylinders comprising a first chamber and a second chamber, at least four hydraulic accumulators, and at least a first and a second fluid communication path. The first chamber of said first hydraulic cylinder and the second chamber of said second hydraulic cylinder are in fluid communication with each other by means of said first fluid communication path, and the first chamber of said second hydraulic cylinder and the second chamber of said first hydraulic cylinder are in fluid communication with each other by means of said second fluid communication path, wherein a first hydraulic accumulator of said at least four hydraulic accumulators is in fluid communication with said first fluid communication path by means of a first accumulator fluid communication path and a second hydraulic accumulator of said at least four hydraulic accumulators is in fluid communication with said first fluid communication path by means of a second accumulator fluid communication path, wherein a connection point between the first accumulator fluid communication path and the first fluid communication path is distanced from a connection point between the second accumulator fluid communication path and the first fluid communication path, and wherein a third hydraulic accumulator of said at least four hydraulic accumulators is in fluid communication with said second fluid communication path by means of a third accumulator fluid communication path and a fourth hydraulic accumulator of said at least four hydraulic accumulators is in fluid communication with said second fluid communication path by means of a fourth accumulator fluid communication path, wherein a connection point between the third accumulator fluid communication path and the second fluid communication path is distanced from a connection point between the fourth accumulator fluid communication path and the second fluid communication path. The first fluid communication path has at a portion of the extension between the connection point to said first accumulator fluid communication path and the connection point to said second accumulator fluid communication path a cross-sectional area that is smaller than the smallest cross-sectional area of each one of:                the extension between the connection point to said first accumulator fluid communication path and said first chamber of said first hydraulic cylinder,        the extension between the connection point to said second accumulator fluid communication path and said second chamber of said second hydraulic cylinder, and        the first and second accumulator fluid communication paths,        
and
the second fluid communication path has at a portion of the extension between the connection point to said third accumulator fluid communication path and the connection point to said fourth accumulator fluid communication path a cross-sectional area that is smaller than the smallest cross-sectional area of each one of.                the extension between the connection point to said third accumulator fluid communication path and said first chamber of said second hydraulic cylinder,        the extension between the connection point between said fourth accumulator fluid communication path and said second chamber of said first hydraulic cylinder, and        
the third and fourth accumulator fluid communication fluid paths.
By providing a smaller cross-sectional area at least along a part of the extension of the respective fluid communication paths, as described above, means that in use the maximum flow rate between said first accumulator and said first chamber of said first hydraulic cylinder will be higher than the maximum flow rate between said first accumulator and said second chamber of said second hydraulic cylinder. Similarly, the maximum flow rate between said second accumulator and said second chamber of said second hydraulic cylinder will be higher than the maximum flow rate between said second accumulator and said first chamber of said first hydraulic cylinder, the maximum flow rate between said third accumulator and said first chamber of said second hydraulic cylinder will be higher than the maximum flow rate between said third accumulator and said second chamber of said first hydraulic cylinder, and the maximum flow rate between said fourth accumulator and said second chamber of said first hydraulic cylinder will be higher than the maximum flow rate between said fourth accumulator and said first chamber of said second hydraulic cylinder. Therefore, the fluid in the first hydraulic accumulator will, when a sudden event occurs, be able to travel to the first chamber of the first hydraulic cylinder, the fluid in the second hydraulic accumulator will be able to travel to the second chamber of the second hydraulic cylinder, the fluid in the third hydraulic accumulator will be able to travel to the first chamber of the second hydraulic cylinder and the fluid in the fourth hydraulic accumulator will be able to travel to the second chamber of the first hydraulic cylinder at a higher flow rate, as compared to the other chamber they are in respective fluid communication with. In a similar manner will the fluid in the first chamber of the first hydraulic cylinder be able to travel to the first fluid accumulator at a higher flow rate than what is possible for the fluid in the second chamber of the second hydraulic cylinder, the fluid in the second chamber of the second hydraulic cylinder will be able to travel to the second fluid accumulator at a higher flow rate than what is possible for the fluid in the first chamber of the first hydraulic cylinder, the fluid in the first chamber of the second hydraulic cylinder will be able to travel to the third fluid accumulator at a higher flow rate than what is possible for the fluid in the second chamber of the first hydraulic cylinder; and the fluid in the second chamber of the first hydraulic cylinder will be able to travel to the fourth fluid accumulator at a higher flow rate than what is possible for the fluid in the first chamber of the second hydraulic cylinder. Hence, when a sudden event that affects one or both of the hydraulic cylinders occurs, the reduced cross-sectional areas of the fluid communication paths dampen or delay the cross-coupling between the cylinders. However, as the cross-sectional areas are only reduced, a cross-coupling still exists and fluid will be able to flow in the fluid communication paths to the other one of said chambers even if the flow will be lower than if there would not have been a reduced diameter provided. When events that are not so sudden occur the reduced diameter will be able to handle the required flow rate and therefore, the cross-coupling will continue to work as a hydraulic anti-roll bar in such situations.
The hydraulic suspension system according to this first aspect of the invention is suitable to use as a suspension for a vehicle. The first hydraulic cylinder is adapted to be connected to one side of a vehicle frame, and the second hydraulic cylinder is adapted to be connected to the other side of a vehicle frame.
With fluid communication paths and accumulator fluid communication paths are meant to understand any combination of e.g. hydraulic lines, such as pipes, hose, channels, etc. that may be used alone or in combination to connect at least two hydraulic cylinders and two hydraulic accumulators.
With cross-sectional area of fluid communication paths and accumulator fluid communication paths is meant to understand the flow area of the communication paths, and not the area of the material defining the communication path.
According to one embodiment, each one of the first and second fluid communication paths comprises hoses connecting the respective sides of the cylinders with a respective accumulator block. Each accumulator block is in fluid communication with two hydraulic accumulators and comprises internal channels connecting the accumulators with the hoses. Hence, according to this embodiment, each one of the first and second communication paths comprises a first hose connected to one chamber of a cylinder and the accumulator block, and a second hose connecting the accumulator block with a second chamber of the other cylinder.
There exist different types of hydraulic cylinders, e.g. cylinders with one piston rod and cylinders with two piston rods. In cylinders with only one piston rod, the first chamber may be the piston side chamber and the second chamber may be the piston rod side chamber. In such cylinders, both the area and the volume are usually smaller of the piston rod side chamber than of the piston side chamber, because a part of the volume is taken up by the piston rod. In cylinders with two piston rods, i.e. double-rod cylinders, the volume and area of the first and second chambers may be the same.
According to one embodiment, the system comprises a first and a second flow restriction element, which are arranged at the first and second fluid communication paths and at a position between the connection points to said first and second hydraulic accumulators and the connection points to said third and fourth hydraulic accumulators, respectively.
Providing the smaller cross-sectional areas by first and second flow restriction elements has proven to be a simple and yet efficient manner to provide a reduced diameter and cross-sectional area of the fluid communication paths at the desired positions and thereby achieve the desired effect. Providing the flow restriction elements at the fluid communication paths is beneficial as it provides the desired smaller flow rate without reducing the flow rate between e.g. an accumulator and the chamber of a hydraulic cylinder that the accumulator should not have a restricted communication with.
According to one embodiment, each one of the flow restriction elements is provided at a respective one of a channel in an accumulator block.
According to one embodiment, each one of the flow restriction elements has a diameter of 5-15 mm, more preferably of 8-12 mm and most preferably of 10 mm.
According to one embodiment, the diameter of the remaining parts of the fluid communication paths has a diameter of 20-40 mm, and more preferably of 25-32 mm.
According to one embodiment, the first and second flow restriction elements are fixed restrictions. Fixed restriction elements are advantageous in that they provide a decreased flow rate in a simple and cost-efficient manner.
According to one embodiment, the first and second flow restriction elements are variable restriction valves. Variable restriction valves are advantageous in that they provide for the possibility to adjust or tune the characteristics of the hydraulic suspension system. It is for example conceivable with embodiments in which it is possible to adjust the characteristics before starting to drive. The suspension system may then be tuned for certain known driving conditions. It is also conceivable with embodiments in which it is possible to adjust the flow restrictions elements during driving.
According to one embodiment, the first and third accumulators have a larger volume than the second and fourth accumulators, respectively. The size of the hydraulic accumulators should be balanced against the respective displacement volume of the first chamber and the second chamber of the respective cylinders. As the second chamber in certain cylinders, i.e. cylinders with only one piston rod may be smaller, due to the fact that the piston rod takes up a certain space, it may be beneficial to provide the first and third accumulators with a larger volume than the second and fourth accumulators.
According to one embodiment, the first and third accumulators have the same size, and the first and fourth accumulators have the same size. Providing the same size of the first and third accumulators and of the first and fourth accumulators, respectively, is beneficial as it provides for similar spring characteristics of both hydraulic cylinders.
According to one embodiment, the size of each one of the first and third accumulators is within the range of 4 to 7 liters, preferably about 5 liters. According to one embodiment, the size of each one of the second and fourth accumulators is within the range of 2 to 5 liters, preferably about 3 liters. The volumes specified for the above-mentioned embodiments, have proven to be beneficial in order to achieve good characteristics of the hydraulic suspension system, when used in e.g. an articulated hauler. The vehicle according to the second aspect of the present invention comprises a hydraulic suspension system according to any one of the embodiments of the first aspect. The hydraulic suspension system according to the first aspect of the present invention may beneficially be used in a vehicle such as e.g. a work machine, a truck, a bus or a car.
The piston of each of the hydraulic cylinders may then be connected to a respective one of the wheels of the vehicle, and the piston rod may be connected to the frame of the vehicle. It is however also conceivable with connecting the wheels to a respective piston rod, and the frame of the vehicle to a respective piston.
According to one embodiment, said vehicle is a work machine, such as an articulated hauler. The present invention is beneficial to use in an articulated hauler.
According to one embodiment, said first hydraulic cylinder is connected to the left front wheel of said vehicle, and said second hydraulic cylinder is connected to the right front wheel of said vehicle.
Providing a cross-coupled hydraulic suspension system between the two front wheels of e.g. an articulated hauler is beneficial as it provides for good travel comfort for the driver. A hydraulic suspension system according to the first aspect of the present invention may also be provided at other wheels of the articulated hauler as well.
The method according to a third aspect of the present invention is directed to damping an anti-roll function of a hydraulic suspension system for a vehicle, wherein said hydraulic suspension system comprises at least a first hydraulic cylinder and a second hydraulic cylinder, wherein each of said hydraulic cylinders comprises a first chamber and a second chamber and wherein said hydraulic cylinders are cross-coupled to each other, and said hydraulic suspension system also comprises at least four hydraulic accumulators. The method comprises providing a potential maximum flow rate for the hydraulic fluid between the first chamber of the first hydraulic cylinder and a first one of said hydraulic accumulators that is higher than the potential maximum flow rate between said first accumulator and the second chamber of the second hydraulic cylinder, providing a potential maximum flow rate for the hydraulic fluid between the second chamber of the second hydraulic cylinder and a second one of said hydraulic accumulators that is higher than the potential maximum flow rate between said second accumulator and the first chamber of the first hydraulic cylinder, providing a potential maximum flow rate for the hydraulic fluid between the first chamber of the second hydraulic cylinder and a third one of said hydraulic accumulators that is higher than the potential maximum flow rate between said third accumulator and the second chamber of the first hydraulic cylinder, and providing a potential maximum flow rate for the hydraulic fluid between the second chamber of the first hydraulic cylinder and a fourth one of said hydraulic accumulators that is higher than the potential maximum flow rate between said fourth accumulator and the first chamber of the second hydraulic cylinder.
With a method according to the third aspect of the present invention, the fluid in the first hydraulic accumulator will, when a sudden event occurs, be able to travel to the first chamber of the first hydraulic cylinder, the fluid in the second hydraulic accumulator will be able to travel to the second chamber of the second hydraulic cylinder, the fluid in the third hydraulic accumulator will be able to travel to the first chamber of the second hydraulic cylinder and the fluid in the fourth hydraulic accumulator will be able to travel to the second chamber of the first hydraulic cylinder at a higher flow rate as compared to the other chamber each hydraulic cylinder is connected to. In a similar manner will the fluid in the first chamber of the first hydraulic cylinder be able to travel to the first fluid accumulator at a higher flow rate than what is possible for the fluid in the second chamber of the second hydraulic cylinder; the fluid in the second chamber of the second hydraulic cylinder will be able to travel to the second fluid accumulator at a higher flow rate than what is possible for the fluid in the first chamber of the first hydraulic cylinder; the fluid in the first chamber of the second hydraulic cylinder will be able to travel to the third fluid accumulator at a higher flow rate than what is possible for the fluid in the second chamber of the first hydraulic cylinder; and the fluid in the second chamber of the first hydraulic cylinder will be able to travel to the fourth fluid accumulator at a higher flow rate than what is possible for the fluid in the first chamber of the second hydraulic cylinder. Hence, when a sudden event that affects one or both of the hydraulic cylinders occurs, the reduced cross-sectional areas of the fluid communication paths dampen the cross-coupling between the cylinders. However, as the cross-sectional areas are only reduced, a cross-coupling still exists and fluid will be able to flow in the fluid communication paths to also the other one of said hydraulic cylinders even if the flow will be lower than if there would not have been a reduced diameter provided. When events that are not so sudden occur the reduced diameter will be able to handle the required flow rate and therefore, the cross-coupling will continue to work as a hydraulic anti-roll bar in such situations.
According to one embodiment, said method further comprises providing a first flow restriction element between a first one of said hydraulic accumulators and a second one of said hydraulic accumulators, and a second flow restriction element between a third one of said hydraulic accumulators and a fourth one of said hydraulic accumulators.
The provision of flow restriction elements has proven to be a simple and yet efficient manner in reducing the cross-sectional area, and thereby the maximum potential flow rate, of a fluid connection path.